1. Field of the Invention
The present invention relates to a linear solenoid for a vehicle.
2. Description of Related Art
A solenoid control valve is installed as a solenoid device in a vehicle to control, for example, a hydraulic automatic transmission. A linear solenoid plays an important role in the solenoid control valve.
This kind of linear solenoid is disclosed in, for instance, Japanese Unexamined Patent Publication No. 2006-307984A (corresponding to US 2006/0243938A1) and will be described with reference to FIG. 9. An exemplary solenoid hydraulic pressure control valve for an automatic transmission will be described with reference to FIG. 9. The hydraulic pressure control valve of FIG. 9 includes a spool valve 101 and a linear solenoid 102. The linear solenoid 102 drives the spool valve 101.
The linear solenoid 102 includes a coil device 110, a plunger 120 and a magnetic stator 130. The coil device 110 is configured into a tubular form and receives a solenoid coil 112b. The plunger 120 is electromagnetically driven by the coil device 110. The magnetic stator 130 forms a magnetic circuit, which drives the plunger 120. The magnetic stator 130 includes a yoke 131 and a stator core 135. The yoke 131 covers an outer peripheral surface of the coil device 110. The magnetic stator 130 receives the plunger 120 in an axially slidable manner.
A control device 200 controls the current value of the electric current supplied to the coil device 110 in a variable manner to axially drive the plunger 120, so that the valve position of the spool valve 101 is changed.
The electric power supply from the control device 200 to the coil device 110 is implemented by inserting an electrical conductor cord 200a, which extends from the control device 200, into pin type terminals 110a, which are insert molded in the coil device 110.
In general, the coil device 110 is assembled as follows. That is, the coil device 110 is fitted over the stator core 135 of the magnetic stator 130, which is in turn inserted into the cup shaped yoke 131. Then, an opening of the yoke 131 is fixed to a casing (fixing member) of the spool valve 101.
Therefore, the coil device 110 and the stator core 135 need to be loosely fitted together due to the required manufacturing tolerances and/or the assembling tolerances, which limit interference between the coil device 110 and the stator core 135.
With respect to the above described type of the linear solenoid, besides the above cord type, there has been also proposed a rigid type electrical connection between the linear solenoid and the control device. In the case of the rigid type electrical connection, each of the terminals is configured into a strip form, and these terminals are directly connected together. However, in the case of the rigid electrical connection, it has been believed that a robust electrical connection can be implemented. However, when the terminals are worn after a long time use, a contact failure may occur at the electrical connection between the terminals.
Through various experiments and studies for the above disadvantage, it has been found that a gap, which is formed between the coil device 110 and the stator core 135, causes a resonance phenomenon of the coil device 110, thereby resulting in the above disadvantage. Particularly, an axial length of the linear solenoid 102 is unavoidably lengthened due to its need for axially driving the plunger 120. Therefore, under severe driving conditions, such as driving of the vehicle on a rough dirt road for a long period of time, the resonance phenomenon discussed above may cause damage to the terminals and/or unintended disconnection between the terminals in the worst case, thereby possibly resulting in an uncontrollable state of the linear solenoid 102.
In the case of the rigid type electrical connection, in view of the above disadvantage, it has been proposed to provide a vibration absorbing or dumping function to the terminals. However, such a function has not been implemented for practical use.
In the case of the cord type electrical connection using the cord 200a, due to the flexibility of the cord 200a, the cord 200a can absorb or dump the vibrations of the coil device 110. However, the cord 200a may possibly be unexpectedly disconnected due to the above resonance phenomenon. Thereby, it is necessary to provide countermeasures for the above disadvantage in view of a reliability of the electrical connection.